The present invention relates to an apparatus for molding a recorded disc having a molded-in center hole, and more particularly to such an apparatus having a center hole forming pin with good wear and heat conducting properties.
In making high density information recorded discs, it has been found desirable to provide the discs with a relatively large center hole, i.e. about 1.5 inches (3.8 cm) in diameter. Although such holes can be punched through the disc after it is molded, it is more desirable to be able to form the hole as the disc is being molded. U.S. Pat. No. 4,327,047, to M. L. McNeeley, issued Apr. 27, 1982, entitled "Method for Producing Disc Records Having Molded-In Center Holes" describes an apparatus and method for molding-in a large center hole in the disc. As described in this patent, the disc molding apparatus includes a center hole forming pin having a recess in its end and a passage therethrough through which steam can flow to directly heat the pin.
One of the problems with the center hole forming pin shown in U.S. Pat. No. 4,327,047 was that when it become worn after a number of operating cycles the entire pin had to be replaced. To overcome this problem a center hole forming pin has been developed which includes a rod having a passage therethrough to its end and a cap secured to the one end by a screw. The cap is of a material which is harder than the rod and it has a recess in its end surface. The passage in the rod is for a heating medium. This center hole forming pin is shown and described in the patent application of John J. Prusak, Ser. No. 310,856, filed Oct. 13, 1981, entitled "Apparatus for Compression Molding Recorded Discs" now U.S. Pat. No. 4,362,492 issued Dec. 7, 1982 and assigned to the assignee of the present application. The cap being of a hard material has a longer life and when it becomes worn can be easily replaced. However, this center hole forming pin has the disadvantage that by adding the cap additional metal is placed between the end of the passage for the heating medium and the end of the center hole forming pin so as to affect the proper heating of the end of the pin.